1. Field of the Invention
The invention relates to a multilayer wiring board using a core substrate and a method of producing the multilayer wiring board.
2. Description of the Related Art
A conventional multilayer wiring board generally has a core substrate and multilayers of wiring line patterns formed on the core substrate by a process such as buildup process. Most core substrates are made up of a woven or unwoven fabric of glass or an organic material impregnated with a resin material such as epoxy, and often called a resin substrate. The core substrate is provided with holes piercing the substrate in the direction of its thickness, and the wiring line patterns on both sides of the core substrate are electrically connected through a conducting member formed on the inside wall of the piercing hole by plating or the like.
When piercing holes are formed in a core substrate, they were hitherto formed by drilling or laser beam machining, after which a conducting member is formed on the inside wall of the piercing hole by electroless and electrolytic plating with copper. When the piercing holes are formed in the core substrate by drilling or laser beam machining, they are made one by one and, accordingly, even if a large-sized resin substrate is used to produce a plurality of core substrates at a batch, there have been problems in terms of processing efficiency and processing cost. Thus, a method of forming the piercing holes by drilling or laser beam machining has technical limitations and limitations in terms of production efficiency even when small holes are formed, and is not useful for a product having piercing holes formed at a high density and in large numbers.
In the case of a resin substrate made up of a woven or an unwoven fabric of glass or an organic material impregnated with a resin material, peeling is caused between the fabric and the resin material by stress and heat during drilling or laser beam machining, resulting in a poor insulation resistance of the substrate, and preventing the formation of piercing holes at a higher density.
An object of the invention is to provide a multilayer wiring board having conducting members piercing through a core substrate and electrically connecting wiring line patterns on both sides of the core substrate, which members can easily be formed at a high density and in large numbers without subjecting the core substrate to drilling or laser beam machining, and a method suitable for the manufacture of such a multilayer wiring board.
As used herein, the term xe2x80x9cwiring line patternxe2x80x9d means a pattern made of a conductive material in the form of a layer to interconnect different electric or electronic elements or components, which may be located on a layer the same as or different from the layer of the wiring line pattern. Typically, the wiring line pattern in the invention includes, as members thereof, a plurality of lines of conductor material, which may have a portion, frequently called a pad, through which the connection of the line and an element or component is achieved. The wiring line pattern in the invention may include only pad members, which have, in general, a circular or polygonal shape, such as circle or square, and which are connected to an element or component of another layer, such as a via or terminal member commonly used for the connection of elements or components present in different layers. In some cases, a group of the ends of via columns (which are described hereinafter) of a core substrate of a multilayer wiring board, which are exposed at a surface of the multilayer wiring board, is regarded as a wiring line pattern.
The invention provides a multilayer wiring board having a core substrate and wiring line patterns formed on both faces of the core substrate, the core substrate having conducting members piercing through the core substrate, and members of the wiring line patterns on both faces of the core substrate being connected with each other through the conducting member piercing through the core substrate, wherein the core substrate comprises via columns and conductive structural members which are formed by plating, and an insulating structural member which electrically insulates the individual via columns and conductive structural members from each other, the via column piercing through the core substrate and serving as the conducting member for connecting the members of the wiring line patterns on both faces of the core substrate with each other.
The core substrate in the multilayer wiring board of the invention can have a plurality of layers each comprising the via columns and the conductive structural members which are insulated from each other by the insulating structural member, the layers being separated from each other by an insulating layer interposed therebetween, and the via columns of adjacent layers being connected with each other by an intermediate via piercing through the interposed insulating layer.
Selected conductive structural members of adjacent layers can be connected with each other.
At least one of the conductive structural members can be used as a power supply layer (or member) or a ground layer (or member).
Preferably, the insulating structural member is formed of a heat resistant resin material.
A multilayer wiring board of the invention can be produced by a method comprising the steps:
forming a patterned resist film on a surface of a conductor substrate,
plating the surface of the conductor substrate provided with the patterned resist film using the resist film as a mask and the conductor substrate as an electrical power supply layer, to thereby form via columns and conductive structural members,
removing the resist film,
making a core substrate by forming a layer of insulating material on the surface of the conductor substrate so as to expose the top faces of the via columns and conductive structural members, the core substrate comprising the via columns, the conductive structural members, and an insulating structural member resulted from the layer of insulating material,
forming, on the core substrate, a plurality of layers of wiring line patterns, each of which is separated from the underlying core substrate or layer of wiring line pattern by an insulating layer, and
removing the conductor substrate.
One or more members of the wiring line pattern may be connected to the conductive structural member of the core substrate.
It is also possible that layers of wiring line patterns are first formed on a surface of a conductor substrate, a core substrate is then formed on the top layer of wiring line pattern, layers of wiring line patterns are then formed on the surface of the core substrate, and the conductor substrate is removed, to thereby produce a multilayer wiring board having a plurality of layers of wiring line patterns on both sides of the core substrate.